The present invention relates generally to a mowing apparatus of the reciprocating sickle type and more particularly to means for maintaining the sickle bar of such an apparatus in proper cutting relationship with the sickle guards.
The general mode of operation of reciprocating sickle bar mowing apparatus is well known, as is the particular importance of keeping the sickle bar knife sections substantially parallel to the ledger surface on the guards and maintaining proper clearance between them for good shearing action. Some form of holddown clip or plate extending over the knife sections is generally used for this purpose.
Conventional holddown clips, somewhat similar to the slightly modified form illustrated in U.S. Pat. No. 2,203,982 are still widely used, but have not been entirely satisfactory. The difficulty and inconvenience of adjusting such holddown clips often results in mowers being operated with improper knife clearance. Too much clearance allows crop material to force the knife section away from the cutting edges of the guards greatly reducing cutting efficiency. Too small a clearance results in drag on the sickle bar assembly and an increase in wear rate and power required to drive the mowing apparatus. Adjustment is generally accomplished by bending the forward portion of the holddown clip up or down as required by means of a hammer. This method is time consuming and inconvenient and usually requires removal of the sickle bar so that the adjustment must be checked by means of a gauge rather than by direct measurement with the knife in situ. Some attempts at improvement of this type of holddown clip have involved pivoting the clip in a cradle mounted on the frame member and providing screw adjusting means so that the clearance between the forward part of the clip and the sickle section can be varied.
Both the conventional holddown clip and the screw adjusted versions are typically placed between guards where they suffer additional dual disadvantages -- first, of being located so as to snag crop material divided and deflected into this area by the guards, and second, of having only an indirect effect in controlling knife clearances in that they are not directly above the guard ledger surfaces.
Other attempts at improvement have included a variety of less conventional designs including some in which the holddown plate itself is a form of leaf spring or is spring loaded so that there is always holddown pressure on the knife sections although, typically, means are provided for adjusting this pressure. This type of holddown clip is in constant contact with the knife sections and the drag between them increases wear rate and the power required to operate the mowing apparatus.
In another design the holddown clip is centered on the guard and clamped in position with the same screw fastener that retains the guard. Typically, screw adjustment is provided to raise or lower the forward part of the clip but before the screw adjustment can be made, the screw fastener must be loosened to permit pivoting of the holddown clip, consequently loosening the guards and upsetting adjustment of the wear plates between the sickle bar assembly and the frame member.